AU7898681A - Apparatus for measuring the flow rate of molten material - Google Patents

Description

Apparatus for measuring the flow rate of molten material

The present invention relates to apparatus for determining the flow rate of a flow, stream or jet of a molten radiation-emitting material, in particular molten glass or ceramic or mineral materials. When measuring the flow rate of such a flow, stream or jet of molten material having a very high temperature, it is obvious that no mechanical contact between the material and the measuring apparatus is possible. For the purpose of measuring the velocity of a solid elongate object, e.g. a paper web, which moves in the direction of its longtidudinal axis, without mechanical contact between the measuring apparatus and the object, it has previously been proposed that at each of two mutually spaced locations along the movement path of the object there is sensed a signal which originates from or is influenced by that part of the moving object located at that moment at the sensing location, said signal having, for example, the form of light reflected from the object. The signals obtained in this way from the two sens ing locations are of a noise character and are compared with each other in a manner to enable the magnitude of their mutual displacement in time to be established, whereat, when the distance between the two sensing locations is known, said time displacement can be used to determine the velocity of the object. Velocity measuring apparatus of this kind are described, for example in the Swedish Patent Specifications Nos. 329 735, 334 254, 348 055 and 371 015. As will be seen from these patent specifications, velocity measuring apparatus of this, previously known kind are encumbered with serious problem and are relatively complicated, primarily because of the necessity of comparing and determining the relative timedisplacement between two signals of noise character with an accuracy and reliability satisfactory to the measuring result.

It has also been proposed, for example in the German patent specification 2 616 443, the U.S. patent specification 3 388 328 and the British patent specification 1 132 similar apparatus for measuring the velocity of an elongate solid object moving in its axial direction, in which the heat radiation of the object is sensed at two spaced locations along the moving object and the object is locally heated at regular intervals along its length by the application of heat radiation pulses to the object at a location upstream of the sensing locations. However, it is obvious that such an apparatus can not be used for measuring the flow rate of flow, stream or jet of a molten material which is already heated to a very high temperature. Consequently, the object of the present invention is provide an improved, simple and reliable apparatus, which be used for measuring the flow rate of a flow, stream or jet of molten, radiation-emitting material, in particular molte glass or ceramic or mineral materials. The apparatus according to the invention comprises two radiation detectors arranged to receive radiation emitted from a limited section of said material flow at two mutual spaced locations along its flow path and generating electric output signals corresponding to the radiation received, a is characterized in that it further comprises for each of the radiation detectors a signal-processing circuit arranged to receive the output signal of the associated radiation detector for discriminating in said output signal all pulse-like variations exceeding a given smallest amplitude and providing corresponding signal pulses on its output, said pulse-like variations originating from randomly occurring , local deviations in the radiation from the material flow caused by the presence of gas bubbles in the material flow; a time-measuring circuit arranged to receive said signal pulses on the outputs of the signal-processing circuits for measuring the time interval between a signal pulse occurring on the output of the signal-processing circuit associated with the upstream detector and the next occurring signal pulse in time on the output of the signal- processing circuit associated with the downstream detector; and a gating circuit connected between the output of the signal-processing circuit of the upstream detector and the time-measuring circuit for blocking the transfer of any signal pulse occurring on the output of said signal- processing circuit within a given time interval after a preceding occurrence of a signal pulse on said output.

As mentioned in the aforegoing, the invention has been developed for determining the flow rate of a flow, stream or jet of molten radiation emitting material, primarily molten glass or ceramic or mineral materials, for example from the smelter in a machine for manufacturing fibres or filaments of glass or ceramic or mineral materials. The invention is based on the discovery that although, when the radiation emitted by a limited section of a flow, stream or jet of a molten material of this kind, as for instance a glass jet, is detected by means of a radiation detector, a substantial part of the output signal of the radiation detector is of a noise character it also contains pulse- like amplitude excursions, which are of short duration but large magnitude and which occur randomly in time. Figure 1 of the accompanying drawings illustrates by way of example the output signal from a radiation detector arranged to receive radiation emitted from a limited section of amolten glass jet. As illustrated by the figure, the major part of this signal has a noise character, but the signal also contains a plurality of pulse-like and very large intensity variations or amplitude excursions. These pulse-like variations in amplitude originate from local, discrete intensity variations in the radiation emitted from the glass jet, these variations most probably being caused by the presence of gas or air bubbles in the glass jet, parti cularly close to the external surface of the jet. In accordance with the invention, these pulse-like variations in amplitude in the output signals of the two radiation detectors are utilized to measure the flow rate of the glass jet, by applying the output signals of the two detectors to signal processing circuits which discriminate the large amplitude pulses P in the detector output signals, so that said puls only occur on the outputs of the s ignal-process ing circuits, and by measuring the time interval between one such pulse from the upstream radiation detector and the nearest following pulse P in time in the signal from the downstream located detector, which pulse must originate from the same local, discrete deviation in the radiation emitted by the glass jet, and utilizing said time-interval for calculatin the flow rate of the glass jet.

Although, as before mentioned, the invention has primarily been developed for determining the flow rate of a flow, stream or jet of molten glass or ceramic or mineral material, the invention can also be applied in other instances for determining the flow rate of a molten, radiation emitting material, as for instance molten metal, provided that the radiation intensity of the material flow exhibits local, discrete deviations of substantial amplitude at differing loactions along the material flow. If such local, discrete intensity deviations of considerable amplitude do not occur naturally in the material flow, they can be created particularly for measuring the flow rate. This can be achieved, for example, by introducing small gas bubbles into the flow, stream or jet of molten material upstream of the measuring device, said bubbles giving rise to the desired local, discrete intensity deviations in radiation.

The invention will now be described in more detail with reference to the accompanying drawing, in which Figure 1 illustrates the previously discussed output signal from a radiation detector which receives radiation from a limited section of a molten glass jet; and

Figure 2 is an exemplary embodiment of a simplified cir diagram for a measuring apparatus according to the invention Figure 2 illustrates schematically a flow, stream or jet 1 of molten, radiation-emitting material 1, for example a molt glass jet, the flow rate V of which in the direction marke by the arrow in the figure is to be determined. An apparatus according to the invention for determining said flow rate V comprises two radiation detectors S1 and S2, which arranged to receive radiation from two limited sections of the jet 1 located at a suitable distance L from each other along the flow path of the jet 1, via a suitable lens system 2 not shown in detail in the figure. The output signals of the radiation detectors S1 and S2 are each applied to a respective amplifier F1 and F2, from which there are thus obtained signals of the appearance illustrated by way of example in Figure 1 and discussed in the aforegoing. Thus the major part of these signals have a noise character, but also contain large pulse-like amplitude variations P originating from local, discrete deviations in the intensity of the radiation emitted from the glass jet 1. It will be understood that the interval in time T between two pulses following each other in time in the output signals from the radiation detectors S1 and S2, respectively, will constitute a measurement of the flow rate V of the glass jet 1 in accordance with the expression In accordance with the invention, the output signals from the amplifiers F1 and F2 are each applied to a respective signal-processing circuit, which in the illustrated embodiment comprises a Schmitt trigger ST1 and ST2, each of which is arranged to deliver on its output solely s ignal pulses P' corresponding to the pulses P in the input signal which exceed a predetermined amplitude level, for example the amplitude A indicated in Figure 1.

For determining the time interval between two s ignal pulses P' following each other in time from the Schmitttrigger circuits ST1 and ST2, respectively, there is provided a digital counter R, which can be driven from a clock pulse generator C and which has a start input, to which there are applied the signal .pulses P' from ST1, while the signal pulses P' from ST2 are applied to the stop input of the counter. Thus, the counter R is started when a signa pulse P' occurs on the output of ST1, i.e. from the radiation detector S1, and is stopped when the signal pulse P' originating from the same local, discrete intensity deviation in the radiation from the glass j et 1 occurs on the output of ST2, i.e. from the radiation detector S2. As will be understood, the count in the counter R will then constitute a measurement of the time interval between the signal pulses P' from the radiation detectors S1 and S2. The count in the counter R is transferred to a digital calculating and control unit D, which then resets the counter R to zero, so that it can be started by the next signal pulse P' arriving from ST1. The calculating and control unit D uses the aforesaid count in the counter R to calculate the flow rate V of the glass jet 1 in accordance with the aforementioned expression, and transfers the result of the calculation in signal form to a display unit 3 and/or to a controlling data processor or control apparatus 4, for example for controlling or regulating the flow rate of the glass jet 1.

When calculating the flow rate V, the calculating unit D may, to advantage, be designed to utilize the mean value of a plurality of counts transferred from the counter R and each representing the interval in time between two, timewise sequential pulses P in the signals from the radiation detectors S1 and S2, respectively. In this way, the determination of flow rate will be less sensitive to variations in the rise time of the pulses P in the output signals of the radiation detectors S1 and S2.

In order to ensure that the start pulse and stop pulse for the counter R actually originate from the same local, discrete intensity deviation in the radiation emitted by the glass jet 1, the start pulses from ST1, i.e. from the radiation detector S1, are applied to the start input of the counter R via a gating circuit B, which is opened or enabled to allow through a new pulse P' from ST1 only after a predetermined time interval after the appearance of a preceding start pulse P' from ST1. This time interval is selected that it corresponds at least to the maximum expected time for movement of the glass jet 1 over the distance L between the measuring locations of the two radiation detectors S1 and S2.

Claims (5)

C L A I M S

1. Apparatus for measuring the flow rate of a flow, stream or jet (1) of a molten, radiation-emitting material, comprising two radiation detectors (S1, S2) arranged to receive radiation emitted from a limited section of said material flow (1) at two mutually spaced locations along its flow path and generating electric output signals corresponding to the radiation received, characterized in that it further comprises for each of the radiation detectors (S1, S2) a signal-processing circuit (ST1, ST2) arranged to receive the output signal of the associated radiation detector for discriminating in said output signal all pulse-like variation (P) exceeding a given smallest amplitude and providing corresponding signal pulses (P') on its output, said pulse-like variations (P) originating from randomly occurring, local deviations in the radiation from the material flow (1), caused by the presence of gas bubbles in the material flow a time-measuring circuit (R, C) arranged to receive said signal pulses (P') on the outputs of the signal-processing circuits (ST1, ST2) for measuring the time interval between a signal pulse (P') occurring on the output of the signal-processing circuit (ST1) associated with the upstream detector (S1) and the next occurring signal pulse (P') in time on the output of the signal-processing circuit (ST2) associated with the downstream detector (S2); and a gating circuit (B) connected between the output of the signal-processing circuit (ST1) of the upstream detector (S1) and the time-measuring circuit (R, C) for blocking the transfer of any signal pulse occurring on the output of said s ignal processing circuit (ST1) within a given time interval after a preceding occurrence of a signal pulse on said output.

2. Apparatus according to claim 1, characterized in that said time-measuring circuit includes a digital counter (R) driven at a constant frequency and arranged to be started by signal pulses (P') received from the s ignal-processing circuit (ST1) of the upstream detector (S1) and to be stopped by signal pulses (P') received from the signal- processing circuit (ST2) of the downstream detector (S1) to be reset to zero before each renewed start.

3. Apparatus according to claim 2, characterized in that it includes a digital calculating unit (D) arranged to receive the count in said counter (R) after each stop, an to calculate flow rate of the material flow (1) on the basis of said count and the distance (L) between the twomeasuring locations and to generate a signal representative of the calculation.

4. Apparatus according to claim 3, characterized in that the calculating unit (D) is arranged to base said flow rate calculation on the mean value of a plurality of count transferred from said counter (R).

5. Apparatus according to any one of claims 1 - 4, characterized by means arranged upstream of said upstrem detector, for introducing gas bubbles into the molten material.